The subject matter disclosed herein relates to slip rings for wind blade pitch control motors employed in wind turbines.
Most wind turbines are horizontal-axis propeller type systems. Vertical-axis systems, such as the eggbeater like Darrieus and S-rotor type Savonius type systems, are also utilized but are generally more expensive. A horizontal-axis wind turbine consists of a rotor, a gearbox, a generator, a mainframe, and, a generator frame. The rotor captures the kinetic energy of the wind and converts it into rotary motion to drive the generator. The rotor usually consists of two or three blades, with three blades being the more common configuration. A speed-enhancing gearbox is typically used to drive the generator. The gearbox is capable of taking the main rotor speed from 10 or 20 revolutions per minute (RPM) and enhancing it to 2000 or 3000 RPM for more efficient generator operation.
Pitch control is a mechanism to prevent turbine rotor overspeed and potential damage to the turbine. A slip ring assembly is commonly used to control pitch. The slip ring assembly generally includes three high current rotors and numerous small, low current, rotors. The rated capacity of the high current rotors is typically 50 amps at 400 volts. A pitch controller box (the “black box”) contains the logic circuitry that controls the pitch of the blades and is typically placed inside the rotor and receives input signals from the smaller rotors on the slip ring. The slip ring assembly for the pitch control is attached to the back of the gearbox with brackets and senses turbine rotor speed from a shaft within the gearbox. When the pitch controller box senses over-speed from the slip ring's output, it signals the pitch control motors, also located in the turbine hub, to change the pitch of the turbine blades, thereby reducing turbine rotor speed. It does this without twisting the electrical output wires from the machine. The output from the high current slip ring rotors goes to the pitch control motors. The input to the slip rings is from the gearbox shaft that senses real-time turbine rotor speed.
One of the problems with current wind turbines that employ slip rings for pitch control is wear, which can result in wind turbine failures due to arcing between electrical inputs. These failures result in turbine down time, which means a loss in revenue stream for turbine owners in addition to the cost for replacing failed hardware. Prior art repair methods generally include replacing the electrical inputs.
Accordingly, there remains a need in the art for improved slip rings that are less prone to wear and minimize the need to replace the electrical inputs.